Western Michigan University ScholarWorks at WMU Paper Engineering Senior Theses Chemical and Paper Engineering 4-1969 The Effects of pH on Alkaline Sizing of Bleached Hardwood Pulps with Aquapel David K. DeKam Western Michigan University Follow this and additional works at: https://scholarworks.wmich.edu/engineer-senior-theses Part of the Wood Science and Pulp, Paper Technology Commons Recommended Citation DeKam, David K., "The Effects of pH on Alkaline Sizing of Bleached Hardwood Pulps with Aquapel" (1969). Paper Engineering Senior Theses. 143. https://scholarworks.wmich.edu/engineer-senior-theses/143 This Dissertation/Thesis is brought to you for free and open access by the Chemical and Paper Engineering at ScholarWorks at WMU. It has been accepted for inclusion in Paper Engineering Senior Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact wmu- [email protected]. THE EFFECTS OF pH ON ALKALINE SIZING OF BLEACHED HARDWOOD PULPS WITH AQUAPEL by David K. DeKam A report submitted to Dr. s. Kukolish in partial fulfillmept of the requirements for Course 471 Western Michigan University Kalama�oo, Michigan April 14, 1969 ABSTRACT The effects of pH on alkaline sizing of two bleached hardwood pulps, kraft and sulfite, was in­ vestigatedo The pulps were refined in a Noble and Wood cycle beater and handsheets were made with a Noble and Wood handsheet making system. The hand­ sheets were internally sized with 0.15 percent Aqua­ pel using Oo05 percent Kymene 557 as a retention aid. Upon varying the pH of sizing of bleached hardwood sulfite pulp the Hercules Ink Photometer measurements of 258, 636, and 563 seconds were observed at PE�s of 7oO, 805, and 9.5 respectivelyo The sizing increased with pH up to a certain pH value and thsidecreased with a further increase in pHo The Ink Photometer measure­ ments were higher for bleached hardwood kraft pulp, 291 secondJat 7.0 pH and 846 at 8.5 pH, indicating a higher alkaline sizing efficiency for the bleached Rraft pulp over this pH range o TABLE OF CONTENTS PAGE THEORY AND HISTORICAL BACKGROUND ••••••••••••• o. 1 EXPERIMENTAL SECTION..... .• .. .• .• . •• . .. .• • •• . 6 Experimental Objectives ••••••••••••••••••• 6 Experimental Design ..•..•••••.•.•..•••.•.• 7 Experimental Procedure... •• •• • • . • .• . •. • . 9 DISCUSSION. • . • • • • • • • • • . • . • . • • • • • • • • • . • • • • • • . l:;E: Optimum Sizing Freeness................... 1:2 pH Effect on Alkaline Sizing of Bleached Hardwood Pulps.............. 16 Comparison of the Ease of Alkaline Sizing of Two Bleached Hardwood Pulps ••••••••••••••••••••••• 18 CONCLUSIONS.. • . • . • . • • . • . 20 LITERATURE CITATIONS •••••.•••••••••••••••.••••.• 21 -1- THEORY AND HISTORICAL BACKGROUND In the early history of papermaking, when the product was used only for writing and printing, the need to limit the spreading of ink resulted in sizing the paper with gelatinous vegetable materials which had the effect of sealing or filling the surface pores. Later, the term sizing was applied to the treatment of paper stock prior to the formation of the sheet with water-repellant materials such as rosin or wax; this is known as internal sizing. The use of paper for wrapping and packaging brought additional requirements in pro­ tecting the contents from fluid transfer through the paper. In some cases this has resulted in the demand for complete resistance to fluid penetration. By nature, cellulose fibers'are hydrophilic. So depending upon the amount of beating and sheet porosity paper can be quite absorbent toward water and other low viscosity liquids. More viscous liquids such as oil are also absorbed by paper,however, there is doub:t as to whether oil penetration is dependent upon the porosity of paper. The mec_hanism by which sizing brings a bout resistance to penetration by liquids is explained by the following relationship • rrcose ,) R .. til where r is the surface tension of the penetrating liquid, -2- tis the radius of the capillary involved, 'l is the viscosity of the liquid, J. is the length of the cap­ illary and 8 is the contact angle which forms between the solid fiber surface and the liquid (l)o This in­ dicates that decreasing r by beating the pulp and there­ by making a denser paper should improve sizing or decrease penetrationo Hydrophobic, inert sizing agents have a decreasing effect on liquid penetration by increasing the contact angle between the liquid and the fiber surfaceo The pen­ etration rate is related to the contact angle in that if a low contact exists, capillary attraction causes spontaneous entrance of the liquid into the capillary• • However, if the contact angle is greater than 90 , the value of cos 8 becomes negative, and a resisting pressure develops which prevents penetration (2). Of the sizing agents presently used for internal sizing, rosin size is the most common. Several mechan­ isms for rosin sizing have been proposed, but none have been proven. The basic principle is that the negative charge of the rosin particle in solution with cellulose fibers is changed to positive by a sufficient amount of alum which enables it to precipitate onto the neg­ atively charged cellulose fibers o Addition of the alum decreases the pH of a pulp slurry o Rosin sizing is impossible under alkaline conditions, with a pH of 5.0-505 contributing the most ...3_ effective sizing conditions (�) o With the advent of olosed white water systems, excessive build-up of sulfate ion tends to occur if alum alone is used to control the pH, resulting in equipment corrosion and the production of paper having poor aging properties. If alum is reduced to take care of this situation, poor sizing will take placeo Automatic addition of an alka­ line material other than carbonate, while alum is added in the normal manner, is used to combat the sulfate ion build-up in some mills. The pH at which the rosin sizing is done, greatly influences the aging properties of the papero The acid content of the sheet increases as the sizing pH decreases and fiber deterioration increases with the acid contento This presents a problem when paper is sized with rosin in the most efficient pH range. The pH can be increased to reduce the strength loss with aging, however, a hard rosin size must be used if good sizing is desired. This presents additional problems • Paper sized with rosin in the higher, ' pH range yellows on ex- posure to sunligh�. A los,s of aizmgg with aging occurs resulting in an absorbent paper (!}. So one can see the difficulties encountered in attempting to produce a permanent paper and one that won't yellow on ex­ posure to sunlight while sizing under acidic pH con­ ditions. These problems in acid sizing are g�eatly re­ sponsible for the development of polyamide wet strength -4- resins and Aquapel, which permit sizing under alkaline conditionso Aquapel, a product of Hercules Powder Company, is an alkylketene dimer prepared from long­ chain fatty acidso Palmitic (CM. _H,z.01 ) and stearic (C11 H,'-OJ acids are the ones generally used to develop maximum water resistance. When made from stearic acid, Aquapel has the following structure (�): 2 ) C \-i 3 - ( C.:a.) H If -C. lot 2 C - C. '"l - ( a.)C. \it IS -C.W, I \ o-c-o Under neutral or alkaline conditions, the lactone ring of the alkylketene dimer will open and react with materials containing free hydroxyl groups or amide groups. Aquapel's sizing effect results from its re­ action with free hydroxyl groups on cellulose fibers to form an ester, which is water repellant and chemically inert. The reaction of Aquapel with cellulose is R R I l "1,C.- < - C. w � �,o 3) I o t,( o .-( OK O o 1-l O tit,,i O l \ \ l \ l t where R is an alkyl group(�). An undesired side re­ action in this alkaline sizing process is hydrolysis of the alkylketene-dimer (2). 0 II 4) R-C.ij :c - c.H-R + H1,.0--,,, R.-C..\ii..-C.-c.Hi.-� ♦ C.Oz.. I I 0-,20 Aquapel can also react with water to form a ketone, -5- which is of no value in sizing. -6- EXPERIMENTAL SECTION Experimental Objectives The objectives of this investigation were as follows: 1) Determine the optimum sizing freeness for two bleached hardwood pulps, kraft and sulfite o 2) Determine the effect of the pH of the pulp slurry on alkaline sizing efficiency for bleached hardwood pulps. 3) Compare the efficiency of alkaline sizing of the two pulps. .7 ... Experimental Design {See Flow Diagram on Next Page) The experimental work was separated into two parts. First, the optimum freeness {C.S.F.) for alkaline sizing was determined for both bleached hardwood pulps (See Graph I). And second, the results from the first part, the effect of the pH of the pulp slurry on Aquapel sizing efficiency was determined. This was accomplished by sizing the bleached sulfite pulp at three pH values, ?oO, 805, and 9.5, and then testing the sizing of the handsheets on the Hercules Ink Photometer. Also the bleached kraft pulp was sized at two pH levels, ?oO and 8.5� These two levels were sufficient for observing whether the two pulps differed in their ease of alkaline sizing with alkylketenew dimerso Careful control of conditions is of utmost importance in this experiment. 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